Evaluation of aggregate gradation on aggregate packing in porous asphalt mixture (PAM) by 3D numerical modelling and laboratory measurements

The packing conditions of unbound aggregate blends and porous asphalt mixture (PAM) are investigated via comparative studies between mechanistic laboratory measurements versus discrete element method (DEM) algorithmic simulations. Nine aggregate gradations with variations in 2.36-4.75 mm and 6.3-9.5 mm fractions were studied. For PAM, PG-76 binder which is a polymer-modified asphalt was used in the mixture, with compaction by gyratory compactor. Simulation models of unbound aggregate blends and PAMs were built in Particle Flow Code in 3 Dimensions (PFC3D) algorithm simulation. The simulation results were compared with the volumetric measurements of laboratory specimens. The results showed that the proportion of 6.3-9.5 mm fraction does not have notable influence on the aggregate packing structure, while 2.36-4.75 mm size fraction has notable influence. The 2.36-4.75 mm fraction has a tendency to either fill the voids of aggregate packing or affect re-orientation of stone-on-stone interlocking of the coarser fraction. DEM modelling provides a valuable aid to design feasible PAMs with a desired packing condition, which shall be supplemented with limited laboratory verifications. (C) 2020 Elsevier Ltd. All rights reserved.